In recent years, the market demand for mobile communications products increases drastically, and thus wireless communications are developed more quickly. Manufacturers tend to design the wireless network cards, particularly the mini wireless card designed for the USB interface smaller and smaller. Therefore, the space reserved for installing an antenna in such wireless network card also becomes smaller. Further, the internal components of the wireless network card also occupy certain spaces. These factors definitely will restrict the position for installing the antenna in a design for wireless network cards. Since the present wireless local area network (WLAN) specification requires an antenna diversity function for the wireless network cards to prevent any dead spot while using a wireless network card, therefore when a manufacturer designs a general wireless network card, at least two antennas are installed inside the wireless network card. The wireless network card designed for the USB interface is no exception either. Since the size of such wireless network card for the USB interface is getting smaller and smaller in these years, the distance between any two antennas installed in the wireless network card with the USB interface is becoming closer and closer and thus causing an interference of signals between these two antennas and an isolation problem between the antennas.
In view of the foregoing issues, many manufacturers at present adopt a single chip antenna for the design of a wireless network card with the USB interface. The chip antenna is generally made by a low temperature cofired ceramic (LTCC) technology, and features a very small volume and thus can provide a flexible use of the space. However, in the actual practice, it is not exactly so. In general, the installation position of such chip antenna usually cannot be designed according to the best conditions recommended by the numeric analysis, but it requires additional components such as capacitors and inductors that will occupy more spaces unnecessarily. Furthermore, such chip antenna also has the following drawbacks:
1. Since the dielectric constant of the material of the chip antenna is very large, therefore the bandwidth will be insufficient, and thus causing a lower performance to the antenna.
2. Additional material cost and installation procedure are incurred for making such chip antenna.
3. Please refer to FIGS. 1 and 2. Due to the relation between the designed installation position of this type of chip antenna 11, 21 on a wireless network card 10, 20 and the grounding metal surface 12, 22 on its right side produces an isolation effect on the grounding metal surface 12, 22, so that the radiating direction of the antenna shifts to the left. The radiation pattern requires a stronger directionality which will cause dead spots to the use of the wireless network card.
Further, the traditional antenna arrays 30, 40 as shown in FIGS. 3 and 4 comprise four antenna units 31, 41 each. In the basic designed structure of such antenna arrays 30, 40, each antenna unit 31, 41 uses the same phase to feed signals, and each antenna unit 31, 42 has the same shape, size and installed direction, and the distance between every two antenna units is the same, such that the electric current distribution and phase for each antenna unit 31, 41 can be kept equal, and thus effectively enhancing the antenna gain. In other words, the directionality at the free end (or front end) of the antenna unit 31, 41 can be improved effectively.
However, the actual design of an antenna array 30, 40 usually needs to satisfy certain design specifications and application requirements, and it is necessary to vary the quantity, installing position as well as the phase and intensity of the input current, particularly for a wireless network card with a USB interface installed on a mini printed circuit board. Due to the limitations on space and mechanical design, the basic architecture and design concept for the foregoing antenna cannot be applied successfully to such mini printed circuit board from beginning to end, and the directionality for both left and right sides cannot be improved effectively.
Therefore, the present invention designs an ideal antenna array to provide a larger coverage on the use of the wireless network card with a low cost under the conditions of limited space and mechanical restrictions of the mini printed circuit board.